Layout Clamps For Keyways Starrett 298 Seat Clamps - USED Parallel Line Scribing Clamps Made of steel, case hardened and accurately ground, they are 1 long x 7/16 wide (25 x 11mm) and have a 7/64 (2., 8mm) slot width. L.S. STARRETT COMPANY #298 ; SKU # 04965951327 ; Type: Key Seat Clamp ; Material: Hardened Steel Available in pairs only. Key Seat Clamps (Pair). Key Seat Clamps (Pair). STARRETT. Key Seat Clamps (Pair). Part # STA298. $109.00. 1 In Stock. Quantity. 1. Add to cart. Add to list These key seat clamps convert steel rules, combination square blades and straight edges into key seat rules for laying out keyways and scribing parallel lines on round work. Starrett 289B attachment for combination square, Starrett 665E guide Pair of key seat clamps , Unit count: 1., Package Dimensions: 2., 8 L x 8., 8 H x 3., 2 W (centimeters)